Sprue forming pattern

ABSTRACT

A reusable cup-shaped sprue forming pattern to support a disposable investment casting pattern or pattern assembly.

United States Patent Inventor Appl. No.

Filed Patented Assignee Milton 0. Gr0sjean Los Angeles, Calif. 812,581

Mar. 28, 1969 Sept. 14, 1971 The Garrett Corporation Los Angeles, Calif.

SPRUE FORMING PATTERN 2 Claims, 1 Drawing Fig.

U.S. Cl

B226 7/00 Field of Search 164039-249, 244-249 [56] References Cited UNITED STATES PATENTS 1,361,188 12/1920 Schmidt .1 164/244 2,451,747 10/1948 Kindt [64/249 2,994,931 8/1961 Operhall et a1. 164/246 3,177,537 4/1965 Horton 164/244 X 3,401,737 9/1968 Rosenfeld 164/244 Primary Examiner-J. Spencer Overholser Assistant Examiner-John S. Brown ArtorneysAlbert J. Miller and John N. l-lazelwood ABSTRACT: A reusable cup-shaped sprue forming pattern to support a disposable investment casting pattern or pattern assembly PATENTED SEPl 419m 3, 04 495 INVENTOR.

MILTON O. GROSJEAN ATTORNEY SPRUE FORMING PATTERN BACKGROUND OF THE INVENTION In investment casting, the disposable pattern is normally mounted on a cup-shaped wax base, customarily referred to in the industry as a wax cup. This wax cup serves a dual function; first it provides a means to support and handle the pattern during subsequent operations such as forming of the shell mold; and second, it leaves a convenient pouring entrance for the molten metal once the wax cup has been removed from the shell mold.

It has been conventional practice to mold into the bottom of each wax cup a threaded bolt or stud which projects upward into the cup. Alternatively, the, inner peripheral wall of the wax cup can be threaded as described in U.S. Pat. No. 3,401,737. In either case, a handle is easily secured to the threaded stud or wall portion of the wax cup during certain shell mold operations and readily removed between operations.

While the wax cup has served its function well for many years, it has the distinct disadvantage that a new wax cup must be prepared for each wax pattern. This is true whether a threaded stud is molded into the bottom of the wax cup or the inner wall of the cup is threaded.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWING The single FIGURE is a perspective view, partially broken away, of the nondisposable cup-shaped sprue-forming pattern and its associated handle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reusable sprue-forming pattern shown in the single FIGURE is for use in connection with a disposable pattern or pattern assembly 12 for shell-type investment molds. The disposable pattern or pattern assembly 12 does not form a part of the invention and its configuration is unimportant, hence it is shown in diagrammatic form only. It may be a single pattern or may include a plurality of patterns having a gating system to feed the individual patterns. While normally constructed of wax, other disposable materials such as frozen mercury, white metal alloy and polystyrene have been utilized. The sprueforming pattern 10 is generally of a frustoconical shape, commonly referred to as cup shaped since the apex end 14 is normally closed. This apex end 14 may include a smaller end section 16 defining a shoulder 18 to facilitate the mounting of the sprue-forming pattern 10 to the wax pattern 12. A threaded bolt or stud 20 is integrally positioned in the apex end 14 of the pattern 10 and extends a short distance into the interior of the cup-shaped pattern 10.

The open end 22 of the cup-shaped pattern 10 may terminate with an annular flange 24. The outer surface of the cup-shaped pattern between the apex end 14 and open end 22 can be that conforming to a surface traced by a moving right line. Alternately, the outer surface may be configurate in many different shapes to meet different sprue requirements. In any case, this outer surface should be smooth and highly polished.

The pattern 10 may be constructed of any lightweight structural material such as aluminum, magnesium, zinc, steel and other similar metals or their alloys plus selected plastics. The basic considerations are weight, surface smoothness, repairability, and com atibility with investment casting dewaxing materials. The t readed stud 20 may be cast directly into the pattern when the pattern is being formed.

The sprue-forming pattern 10 is utilized in connection with a handle 26 which supports both the sprue-forming pattern 10 and the wax pattern 12 mounted thereon. The handle 26, which may be a pipe or tube, has internal threads at one end thereof to cooperate with the threaded stud 20. Simply turning the handle 26 will affect the connecting or disconnecting of the sprue-forming pattern 10 and associated wax pattern 12. With the handle 26 secured to the threaded stud 20 of the sprue-forming pattern 10 upon which the Wax pattern is mounted, conventional shell-molding techniques, not a part of this invention, are utilized to build up a shell mold around both the wax pattern 12 and the sprue-forming pattern 10. During this shell mold forming, the handle may be easily removed during and/or between certain operations and then replaced when required.

Once the shell mold has been completed and dried around the patterns 10 and 12, the disposable pattern and nondisposable sprue forming pattern are removed from within the shell mold by any conventional technique. Where the disposable material is wax, the shell mold may be simply heated in an inverted position to permit the sprue-forming pattern to fall out and the wax to flow out. The shell may be chilled before this heating to facilitate removal of the wax and pattern 10. Also, the outer surface of the sprue-forming pattern 10 may be coated with a thin coating wax or'with a film release agent to facilitate its removal. With the patterns removed, molten metal can be poured into the shell mold to complete the castmg.

The sprue-forming pattern can be reused with another disposable pattern after it has been removed from the shell mold. This reuse can be continued on an almost sprue-forming limited primarily by the life of the threads on the threaded stud 20. The outer surface of the sprue-forming pattern can be easily maintained in a smooth, highly polished condition. If nicks or other imperfections develop in the outer surface as the result of this continued use, the outer surface can be repolished or remachined to remove the nick. The exact size of the sprue forming pattern is not critical to successful shell mold investment casting and therefore the pattern can be slightly reduced in size in order to remove a nick or other wear-induced imperfection.

While specific embodiments of the invention have been illustrated and described, it is to be understood that these embodiments are by way of example only and that the invention is not to be construed as being limited thereto, but only by the proper scope of the following claims.

lclaim:

1. A reusable sprue-forming pattern for use with an investment casting disposable pattern comprising:

a generally frustoconical, cup-shaped metallic member having a smooth outer surface free of any material thereon, an annular flange extending outward from the open end thereof, and a relatively thick base;

a stud member molded into the base of the cup-shaped member and having a threaded portion extending a short distance into the open interior of the cup-shaped member and terminating well below the open end thereof; and

an elongated hollow handle having one end extending down into the open interior of the cup-shaped member and including internal threads to engage the threaded portion of said stud member at the base of the cup-shaped member.

2. The sprue-forming pattern of claim 1 wherein said cupshaped member is aluminum. 

1. A reusable sprue-forming pattern for use with an investment casting disposable pattern comprising: a generally frustoconical, cup-shaped metallic member having a smooth outer surface free of any material thereon, an annular flange extending outward from the open end thereof, and a relatively thick base; a stud member molded into the base of the cup-shaped member and having a threaded portion extending a short distance into the open interior of the cup-shaped member and terminating well below the open end thereof; and an elongated hollow handle having one end extending down into the open interior of the cup-shaped member and including internal threads to engage the threaded portion of said stud member at the base of the cup-shaped member.
 2. The sprue-forming pattern of claim 1 wherein said cup-shaped member is aluminum. 